refactor: pluginctl v0.1.5-0.20250814142442-19c417d53e1d

[fmartingr]

Summary

Example PR on how to migrate a plugin to pluginctl.

1. Add webapp.config.js and babel.config.js to the manifest props.pluginctl.ignore_assets.
2. Remove build/setup.mk, build/manifest & build/pluginctl.
3. Run pluginctl updateassets.

Migration guide: mattermost/pluginctl#2

Closes: #180

[fmartingr]

@hanzei I've followed the manifest apply approach with pluginctl because that how it was done in the starter template, but this plugin followed another approach (that I liked more, tbh).

Unsure which one is the "appropriate one". Do you have any insight on that?

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